The present invention relates generally to methods of seismic data processing, and more particularly, to methods of enhancing signal-to-noise ratio of seismic data.
The signal-to-noise (S/N) ratio of pre-stack and post-stack seismic data is often poor. Subsequently, this poor S/N ratio can result in very low quality derivative attributes such as gradient sections. Other properties of seismic displays which are also adversely affected by poor S/N ratio include continuity and resolution. Other products derived from seismic data, and which are highly dependent upon S/N ratio, include amplitude versus offset (AVO) attributes, offset sections and final stacks.
AVO attributes, such as gradient sections, are typically extremely noisy compared to stack data. Most commonly this increases the uncertainty in the prediction process (due to scatter), and hence reduces the power of AVO analysis as a clear Direct Hydrocarbon Indicator (DHI). In areas where seismic data quality is poor the attribute sections are often too noisy to be of any significant use. The main causes for this reduction in S/N ratio, and hence degraded attribute estimation, are the presence of coherent and random noise, transmission effects and Normal Moveout (NMO) errors in the seismic data.
There are numerous techniques employed to increase S/N ratio in seismic data. Examples of such techniques to cleanup seismic data prior to calculating derivative attributes include F-X deconvolution, FK filtering, and bandpass filtering.
The method of supergathering helps to increase S/N ratio of seismic data. Seismic data within a supergather are typically summed together. Such supergathering method of seismic data enhancement has serious shortcomings. Because the traces of the entire subregion are averaged together, the traces tend to blur together, i.e. spatial resolution is reduced, and highly distinctive traces are averaged out or significantly reduced.
There is a need for a method which is significantly more effective at improving the signal-to-noise ratio of seismic data while retaining spatial resolution. The present invention addresses this need.
The present invention is a method for processing seismic traces to provide seismic data with enhanced signal-to-noise (S/N) ratio. This allows for improved seismic displays. Further, other downstream products reliant upon seismic data will likewise benefit from the enhanced S/N ratio provided by the present invention.
FIG. 1 shows a flow chart of steps which may be used with the present invention. A seismic survey of traces is obtained which has been collected over an areal region. The seismic survey includes a grid of nodes. Each node ideally is representative of traces from a common reflection point (CRP).
A working subset of traces is selected from a subregion of the areal region. A rolling supergather aperture is used to select the working subset of traces. The rolling supergather aperture is positioned relative to an output node for which modified seismic traces are to be created.
A model subset of traces is selected from the working subset of traces using a predetermined set of rules such that the model subset of traces is selected from proximate the center of the working subregion. Most typically, the set of rules results in the traces from only the center most node of the rolling supergather aperture being selected for inclusion in the model subset of traces. The model subset of traces is composited to ideally form a single model trace.
Next, the individual traces of the working subset of traces are compared and modified with the model trace using an alignment technique. Preferably, a dynamic static correction, such as a time varying trim statics technique, is used to align the original traces to the model trace with a new modified subset of traces being created. Preferably, the modified subset of traces is composited and reduced in size to an enhanced subset of traces having an enhanced signal-to-noise ratio as compared to the original working subset of traces.
The rolling supergather aperture is then incrementally moved such that it is repositioned relative to another of the nodes to thereby select another working subset of traces from the areal region. The steps identified above are repeated to transform the traces of the new working subset of traces into a new modified subset of traces and, ideally, subsequently an enhanced subset of traces. This process is continued until the rolling supergather aperture has covered the entire areal region and enhanced subsets of traces have been created for each output node. The modified seismic survey may then be used to produce an enhanced seismic display.
The present invention further includes a computer-readable medium containing executable code for processing seismic traces to provide seismic data with enhanced signal-to-noise ratio. The code, when executed, ideally performs the above described steps to provide seismic data with enhanced signal-to-noise ratio which may be used to create enhanced display traces.
It is an object of the present invention to use rolling supergathers with a dynamic static correction to significantly improve S/N in pre-stack data and attribute sections.
It is another object of the present invention to improve the quality of attributes to increase the reliability of quantitative amplitude analysis.
It is a further object to provide a method to ensure that a dynamic static solution maintains structure and is an edge preserving process.